Because Helicobacter pylori has strong urease-producing activity, urea labeled with .sup.13 C or .sup.14 C is used for diagnosing stomach infected with Helicobacter pylori. Urea labeled with .sup.13 C or .sup.14 C is prepared as powder, particularly freeze-dried powder, containing urea alone, for oral administration in aqueous solution. The urea labeled with 13C or 14C is degraded by the urease produced by Helicobacter pylori in stomach into carbon dioxide gas labeled with .sup.13 C or 14C, which is then released into expired air. By measuring the concentration of the carbon dioxide labeled with .sup.13 C or .sup.14 C, therefore, the presence or absence of Helicobacter pylori infection can be diagnosed. When the powder is orally given in aqueous solution, the urea labeled with .sup.13 C or .sup.14 C is degraded with urease derived from oral bacterial flora, which causes difficulty in diagnosing correctly Helicobacter pylori infection.
As urea formulations for, diagnosing Helicobacter pylori infection, a capsule of .sup.14 C-urea [The American Journal of Gastroenterology, 91, 233 (1996)] and a substantially water-soluble composition in solid, containing urea labeled with an isotope (W096/14091), have been known.
However, urea has strong cohesion potency and therefore sticks to tableting machines and the like during the tableting process, which results in poor industrial productivity. Tablets containing urea have so poor hardness that it is difficult to produce high-quality tablets of urea.